1. Every node generates it's own blockchain at zero difficulty. It's okay if nodes have different blockchains. What matters is that they all record the same transaction history. Nobody publishes their blockchain anyway.
the whole idea of the blockchain is that everyone is in perfect sync at all times and has the same exact ledger. otherwise if for example i have a transaction output and spend it without telling everyone else then i can spend it more than once and only tell some. and the system will at some point fall apart.
Mining only forces everyone to use the same blockchain which isn't strictly necessary in order for every node to have the same transaction history.
no, actually mining is the process of updating the ledger with new changes in an irreversible way!it is like wanting to spend money from your bank account but not have the bank update your balance! it can't work. each (bank) transaction has to be recorded in their database to update the "ledger" so that if you tried spending more than your balance, the system prevents you.
in bitcoin we don't have balances, we only have transactions that are either spent or unspent. the ledger has to be updated each time through an irreversible costly process called mining so that when a transaction output was spent the subsequent attempts at spending the same thing fails.
